1. Field of the Invention
The invention is directed to an actuating element for a clutch which is actuated by pressure medium, and includes a slave cylinder, a piston that is displaceable in the slave cylinder by the action of pressure medium and a tappet abutting the piston for actuation of a clutch release lever.
2. Description of the Related Art
A prior art pneumatically operating actuating element is disclosed in European reference EP 0 453 749. As is the case with actuating elements which are designed for use with clutches, the piston is at a distance from a rear wall of the slave cylinder housing when the clutch is engaged. Due to wear of the clutch linings, the piston is increasingly displaced toward the rear wall by the tappet supported on it when the clutch is engaged. The lift or stroke area of the piston between the release position and engaging position of the clutch is increasingly shifted in a direction opposite to the actuating direction as the piston is displaced toward the rear wall. Undesirably large release paths of the clutch which may lead to excessive pressing of the clutch spring are prevented in this known actuating element by a distance or path sensor at the actuating element which detects the actuating path of the piston in the driver housing independently from the wear of the clutch linings.
In practice, hydraulically operating actuating elements do not use electronic means for limiting the release path. Rather the slave cylinder is usually actuated by a clutch master cylinder whose piston is movable against a mechanical stop for limiting the maximum amount of pressure medium conveyed into the slave cylinder of the clutch. However, a master cylinder of this type is relatively expensive. It is desirable to apply pressure medium to the slave cylinder directly from a pressure medium source via a clutch valve.